Method and apparatus for generating channel quality information for wireless communication

ABSTRACT

A method and apparatus for generating channel quality information, such as may be used for transmit link adaptation, provide different operating modes, such as a first mode that may be used when propagation channel estimates are not reliable, and a second mode that may be used when the propagation channel estimates are reliable. In one or more embodiments, channel quality information is generated using receiver performance information that characterizes receiver performance in terms of a defined channel quality metric, e.g., supported data rates, for different values of receiver input signal quality over a range of propagation channel realizations. Channel quality information can be generated by selecting channel quality metrics according to receiver input signal quality and a desired probability of meeting a defined performance requirement over a range of propagation channel realizations, or by selecting channel quality metrics according to receiver input signal quality and particularized propagation channel realizations.

BACKGROUND

The present invention generally relates to generating wirelesscommunications, and particularly relates to generating channel qualityinformation.

Channel quality information can be expressed in a number of ways, suchas a channel quality indicator identifying the effective signal qualityof a wireless communication receiver. The effective signal qualityrepresents the benefits of any interference cancellation gains,diversity combining gains, coding gains, etc., that may be provided bythe receiver. In other words, the output signal quality of a givenreceiver may be significantly better than the receiver's input signalquality, which generally is expressed as the “raw,” uncompensated ratioof received signal energy to background noise and interference.

Those skilled in the wireless communications art will appreciate thevalue of generating channel quality information based on the outputsignal quality rather than the input signal quality, because the outputsignal quality better represents the actual signal quality bearing onthe quality of demodulation and decoding performance. That is, assumingthat the channel quality information is used for link adaptation, e.g.,picking the modulation and coding scheme (MCS) that is appropriate fortransmitting to the receiver, using input signal quality rather thanoutput signal quality would result in chronically underutilizing thetransmission link.

Accurately determining output signal quality as part of ongoing receiveroperations is not, however, a straightforward proposition for some typesof receivers. In particular, non-linear receivers generally have acomplex relationship between input signal quality and output signalquality. Examples of non-linear receivers include multi-stage receiversemploying successive interference cancellation, and joint-detectionreceivers.

Further, even assuming the calculability of output signal quality, suchcalculations may be inaccurate under some circumstances. For example,the performance achievable by a given receiver depends on a number ofvariables, including propagation channel conditions. Some channelconditions translate into better receiver performance than others. Thus,even for the same receiver input signal, the receiver output signalquality will vary as a function of changing channel conditions. Ifchannel conditions are changing rapidly, or the input signal is too weakto make reliable channel estimates, reporting output signal quality, orsome metric relating to output signal quality, may lead to controlerrors.

For example, a supporting base station may perform transmit linkadaptation responsive to receiving channel quality information from awireless communication device, that identifies the quality of thechannel in terms of some metric, such as a channel quality indicator, arate selection indicator, or the like. Thus, the base station can adjustthe transmit data rate, for example, in accordance with the channelquality indicators reported by the device. This control mechanism workswell if the actual channel conditions change slowly in comparison to thelink adaptation control lag. However, performing link adaptation inconsideration of actual propagation channel conditions becomesunreliable if those conditions change rapidly in comparison to the linkadaptation control timing.

SUMMARY

According to one or more method and apparatus embodiments taught herein,different modes of operation are used for determining channel qualityinformation for a wireless communication device, depending on, forexample, the reliability of propagation channel estimates for thewireless communication device. For example, in one embodiment, channelquality information is determined in a first mode by mapping receiverinput signal quality to a data rate that can be supported at a desiredprobability over a range of propagation channel realizations. Asupported data rate may be defined as an allowable data rate that can beachieved with a desired performance requirement, e.g., Block Error Rate(BLER). Further, in the second mode, the channel quality information isdetermined by mapping receiver input signal quality to a data rate thatcan be supported for a particular propagation channel realization, orthat can be supported for a constrained range of propagation channelconditions, corresponding to the current channel estimates obtained bythe wireless communication device.

Thus, the first mode provides for generating channel quality informationas a function of long-term propagation channel conditions whenshort-term propagation channel estimates are not reliable, such as wherethe time lag associated with transmit link adaptation is large comparedto the coherent time of propagation channel fading. Conversely, thesecond mode provides for generating channel quality information as afunction of short-term propagation channel conditions when short-termpropagation channel estimates are reliable. Modal operation can bedriven by determining whether the channel estimates being generated bythe wireless communication device are reliable. Reliability may bedetermined by evaluating the mobility—e.g., rate of movement, Dopplerfrequency, etc.—of the wireless communication device, or by evaluatingthe channel estimates.

With the above in mind, in one embodiment, a method of determiningchannel quality information for a transmit propagation channelassociated with a wireless communication device comprises in a firstmode, generating channel quality information according to a firstalgorithm that does not depend on channel estimates, and in a secondmode, generating channel quality information according to a secondalgorithm that depends on channel estimates. Receiver performance datacharacterizing receiver performance for a type of receiver associatedwith the wireless communication device may be used to generate thechannel quality feedback in the first and second modes, and suchgeneration may be performed by the wireless communication device itself,or by a base station in a supporting wireless communication network.

For example, a wireless communication device or a base station maycomprise one or more processing circuits configured to determine channelquality information for one or more signals received by the wirelesscommunication device, based on, in a first mode, generating channelquality information according to a first algorithm that does not dependon channel estimates, and in a second mode, generating channel qualityinformation according to a second algorithm that depends on channelestimates. The processing circuit(s) are, in one or more embodiments,configured to operate selectively in the first or second mode based onwhether the channel estimates are reliable.

Complementing the above method of channel quality informationgeneration, one embodiment of a receiver performance characterizationmethod comprises, at each of a number of receiver input signalqualities, computing an error rate expected for each of a number ofpropagation channel realizations, and, for each of the error ratescomputed, computing a data rate that can be supported for eachpropagation channel realization at each receiver input signal quality,and, for each receiver input signal quality, computing the cumulativedistribution function (CDF) of the supported data rates corresponding tothe propagation channel realizations. Such performance characterizationdata may be stored by the wireless communication device, or by thesupporting wireless communication network. Generally, the performancecharacterization data is specific for a receiver type, and differentdata can be stored for different receiver types. For example, aparticular type of Generalized RAKE (G-RAKE) or other Minimum MeanSquared Error (MMSE) receiver would have different characterization datathan would a particular type of Joint Detection (JD) receiver.Similarly, different performance characterization data can be stored fordifferent transmit/reception modes (MISO, MIMO, etc.), even for the samereceiver type.

A corresponding method of providing rate adaptation feedback from awireless communication device to a supporting wireless communicationnetwork operates in a first mode by selecting a supported data rateusing the receiver performance data according to a receiver input signalquality corresponding to measurements obtained by the wirelesscommunication device, and a desired probability of achieving theselected data rate for a range of propagation channel realizations. Inthe second mode, the channel quality information is generated using thereceiver performance data by selecting a supported data rate accordingto receiver input signal quality and a particular propagation channelrealization, or a constrained range of the propagation channelrealizations, corresponding to channel estimates obtained by thewireless communication device.

Of course, the present invention is not limited to the above featuresand advantages. Indeed, those skilled in the art will recognizeadditional features and advantages upon reading the following detaileddescription, and upon viewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a base station and a wireless communicationdevice, such as a mobile station, wherein channel quality information isgenerated according to one or more method embodiments taught herein.

FIG. 2 is a logic flow diagram for one embodiment of processing logicfor modal generation of channel quality information.

FIG. 3 is a logic flow diagram for one embodiment of selecting operatingmodes in the context of FIG. 2.

FIG. 4 is a logic flow diagram for another embodiment of selectingoperating modes in the context of FIG. 2.

FIG. 5 is a logic flow diagram for one embodiment of a receiverperformance characterization method.

FIGS. 6 and 7 are graphs depicting receiver performancecharacterizations obtained by the receiver performance characterizationmethod of FIG. 5, for different types of wireless communication devicereceivers.

FIG. 8 is a logic flow diagram for one embodiment of modally generatingchannel quality information using receiver performance data.

FIG. 9 is a block diagram for one embodiment of a wireless communicationdevice that is configured to generate channel quality information.

FIGS. 10 and 11 are block diagrams of embodiments of processing circuitsused in generating channel quality information.

FIG. 12 is a block diagram of one embodiment of a base station that isconfigured to generate channel quality information based on receivingchannel quality measurements for the wireless communication device.

DETAILED DESCRIPTION

FIG. 1 illustrates a base station 10 and a wireless communication device12, wherein the channel quality information generated for the downlinkbetween the base station 10 and the wireless communication device 12 is,in a first mode of operation, not dependent on current propagationchannel estimates, and, in a second mode, is dependent on currentpropagation channel estimates. Thus, the first mode of generatingchannel quality information may be used where estimates of the downlinkpropagation channel are not reliable, such as when the wirelesscommunication device 12 is moving at a high rate relative to the basestation 10, or is otherwise experiencing fast fading conditions, or whenthe received signal strength is too low for reliable channel estimation.

Before describing various embodiments of the above method of generatingchannel quality information, it should be understood that the processinglogic associated with generating the channel quality information can beperformed wholly in the wireless communication device 12, wholly in thebase station 10, or performed cooperatively using both the base station10 and the wireless communication device 12. In all such cases, theattendant processing may be implemented in hardware, software, or anycombination thereof. Moreover, it should be understood that the basestation 10 and the wireless communication device 12 are not limited toany particular configuration, nor are they limited to any particularwireless communications standards or protocols.

For example, in one or more embodiments, the wireless communicationdevice 12 comprises a cellular radiotelephone or other type of mobilestation, configured for operation with a supporting wirelesscommunication network that includes the base station 10. In suchembodiments, the base station 10 may comprise a Wideband CDMA (WCDMA)base station configured to provide High Speed Downlink Packet Access(HSDPA) services.

Correspondingly, the wireless communication device 12 may comprise aWCDMA-based access terminal configured to provide channel qualityinformation, or related feedback, to the base station 10, in support ofadapting downlink transmit data rates to changing reception conditionsat the wireless communication device 12. In general, however, thewireless communication device 12 may comprise a mobile station or othertype of handset, a pager, a Portable Digital Assistant (PDA), a palmtopor laptop computer, or a wireless communication module for use therein,or essentially any other type of communication device.

Keeping the method's broad applicability in mind, FIG. 2 illustrates oneembodiment of a method of generating channel quality information,wherein it should be understood that at least some of the illustratedprocessing steps may be performed in other than the illustrated order.Further, although illustrated as serial processing, actualimplementation of the method may involve concurrent, parallelprocessing, as part of ongoing communication operations. Also, it shouldbe understood that the illustrated processing may be implemented in thebase station 10, the wireless communication device 12, or in somecombination thereof.

Processing “begins” with a determination of whether to operate in afirst mode of generating channel quality information (Step 100). If thefirst mode is selected, processing continues with generating channelquality information according to a first algorithm that does not dependon channel estimates (Step 102). Conversely, if the first mode is notselected, i.e., the second mode of operation is selected, processingcontinues with generating channel quality information according to asecond algorithm that depends on channel estimates (Step 104).

In at least one embodiment taught herein, the first mode of generatingchannel quality information is used during fast fading conditions, orwhenever conditions are such that the short-term channel estimatesobtained by the wireless communication device 12 are “unreliable.” Thesecond mode of generating channel quality information is used duringslow fading conditions, or, more generally, whenever the channelestimates are reliable. In other words, channel quality information isgenerated as a function of long-term propagation channel characteristicswhen short-term estimates of the channel are not reliable. Conversely,channel quality information is generated as a function of the short-termpropagation channel characteristics when the channel estimates arereliable.

It should be understood that various methods of assessing channelestimation reliability are contemplated herein, and it should beunderstood that conditions deemed to give rise to unreliable channelestimations in one application may not be considered as such in anotherapplication. For example, the reliability of a short-term channelestimate may be viewed in terms of fading speed versus link adaptationcontrol lag. That is, channel estimates may be deemed more or lessreliable in dependence on how quickly channel conditions change relativeto the transmit link adaptations being made. In some embodiments, thelink adaptation lag—i.e., the time between a reported channel qualitymetric and the corresponding transmit link adjustment—may be used toinfluence whether, or to what extent, short-term propagation channelconditions are considered in generating channel quality information.

With such variations in mind, FIG. 3 illustrates one embodiment ofprocessing logic for determining whether to operate in the first orsecond modes of FIG. 2. Modal selection processing “begins” withevaluating propagation channel fading conditions (Step 106). As will bedetailed later herein, the evaluation may comprise assessing thereliability of the channel estimates to determine whether fast-fadingconditions apply. In other embodiments, fast-fading may be recognized byevaluating mobility, such as by evaluating the Doppler frequency shiftof transmissions on the downlink and/or uplink channels between the basestation 10 and the wireless communication device 12. Of course, otherindicators bearing on the reliability of short-term channel estimatesmay be used. For example, certain service areas may make channelestimates inherently suspect, such as radio sectors in downtown or urbanareas.

If fast fading conditions apply (Step 108), channel quality generationoperates in the first mode, wherein channel quality information isgenerated in a manner that is not dependent on channel estimates (Step110). Conversely, if fast fading conditions do not apply, channelquality information is generated in a manner that is dependent onchannel estimates (Step 112).

FIG. 4 illustrates another embodiment of processing logic fordetermining whether to operate in the first or second modes of FIG. 2.Modal selection processing “begins” with evaluating the network usage orload conditions (Step 114). In a lightly loaded wireless network, thereliability of the channel estimates and the derived channel qualityinformation can be compromised even if the propagation channel fadingconditions change slowly or remain static. For example, because ofbursty and fast varying of inter-cell interference that ischaracteristic of a lightly load network, the channel quality and hencethe supportable data rate realized during actual transmission of thedata can be rather different than what was measured prior to thetransmission.

Thus, if the network is lightly loaded (Step 116), it can beadvantageous to select the first mode of determining channel qualityinformation (Step 118). Conversely, if the network is more heavilyloaded, or the loading is otherwise more stable, channel qualityinformation can be determined according to the second mode of operation(Step 119). The selection of which operating mode to use for channelquality information determination can be evaluated and/or applied toindividual wireless communication devices 12, or can be applied to setsor subsets of wireless communication devices 12, within a given sectoror cell of the network. For example, the first mode may be used for somewireless communication devices 12, while the second mode may be used forothers. The determination of which mode to use may be set according tothe service needs of individual wireless communication devices 12, forexample.

Note that this modal selection can be implemented in ways that arenon-transparent or transparent to the wireless communication devices 12.In one embodiment, a base station 10 in the wireless communicationnetwork can instruct one or more devices in a plurality of wirelesscommunication devices 12 to feed back information that is compatiblewith the preferred operating mode. Alternatively, based on the networkload conditions, the base station 10 can receive information supportingthe second mode of operation, but can choose to ignore all or some ofthat information, in favor of operating in the first mode. In otherwords, the base station 10 may choose not to use all of the feedbackthat it receives.

In some circumstances, the radio resource cost required to supportoperation in the second mode is higher than that for operation in thefirst mode. For instance, to support operation in the second mode,feedback generally has to been sent by the wireless communicationdevices 12 more frequently than is required for operation in the firstmode, to reflect changing propagation channel conditions. The amount offeedback also could be larger to describe the propagation channelconditions in sufficient detail for operation in the second mode. Thestrain on the feedback channel is further exacerbated by the fact that aplurality of wireless communication devices 12 simultaneously transmitsfeedback information to the network. Thus, the first mode of operationmay be preferred even when operation in the second mode is viable,simply based on propagation channel condition considerations.

In one or more embodiments, channel quality information determinationconsiders the potentially higher radio resource costs on the feedbackchannel associated with operation in the second mode. More particularly,the second mode of operation can be reserved for contractuallyprivileged devices or services. The privilege level of a givencommunication device 12 can be referenced from a database with theidentification number of the device. Channel quality information can bedetermined according to operation in the second mode for devices withhigher privilege. The contractual requirement of a service can also be afactor in considering the appropriate operation mode. For instance, forservices with stringent delay or jitter requirements such as packetvoice services, the quality of service can be more easily maintained ifchannel quality information is determined according to operation in thesecond mode.

Deciding whether to determine channel quality information according tothe first or second modes of operation also may be adapted totransmission schemes that consist of separable components. Non-limitingexamples of these types of transmission schemes include multi-carrierCDMA and orthogonal frequency division multiplexing (OFDM) transmission.To support operation in the second mode, the amount of feedback canscale directly with the number of separable components, e.g., fourfeedback values for four-carrier CDMA or eighty values for OFDM witheighty frequency resource units. For large packets or data units thatwould occupy entire or large portions of the components, the relativebenefits of operating in the second mode instead of the first mode canbe significantly smaller than for small packets or data units that wouldoccupy small portions of the components. To conserve radio resources, itis therefore advantageous to include packet or data unit lengths as afactor in operating mode selection.

Such operation is, in one or more embodiments, supported by the use ofreceiver performance data that characterizes the performance of thewireless communication device's receiver type over a range ofpropagation channel conditions, such that the performance data indicatesthe expected performance of the receiver over a range of propagationchannel conditions, and for particularized propagation channelconditions. Determining channel propagation conditions for channelquality information determination—e.g., for supportable ratecomputation—may be required for operation in the first and/or secondmodes of operation. For the first operating mode, long-term channelpropagation conditions are determined and, in one or more embodiments,the propagation channel conditions include one or more of the followingquantities: a characterization of the fading speed of the channel (forexample, based on the estimated Doppler frequency, known mobile speed,rate of negative acknowledgements—i.e. NACK rate, . . . ); and anestimate of the power delay profile (PDP) of the propagation channelassociated with the wireless communication device 12, assuming that thePDP does not change quickly over time.

In one or more embodiments, the estimation of long-term propagationchannel conditions is used for any one or more of the followingprocessing actions: construction of a CDF of the achievable(supportable) data rates; selection of an achievable data rate curve CDFfrom a table of CDF curves that most closely matches the estimatedlong-term propagation channel conditions. Thus, it should be understoodthat in one or more embodiments, CDF curves may be predefined. In suchembodiments, the received signal quality and/or long-termcharacterization of the propagation channel associated with the wirelesscommunication device 12 can be used to select a point or range along apredefined CDF curve to identify channel quality information for thewireless communication device 12—e.g., to identify an achievable datarate. In one or more other embodiments, the long-term propagationchannel conditions as estimated are used to partially or whollyconstruct one or more CDF curves, which can then be used to identifyachievable data rates, for example, as a function of measured signalquality at the wireless communication device 12.

In more detail, for purposes of CDF curve construction, the PDP isconsidered a known quantity, and estimates of the delay tap (channel)coefficient values can be generated and used to further determine thepropagation channel realization for the given PDP. At least oneembodiment estimates propagation channel coefficients based on pilot orother measurements, to support characterization of long-term propagationchannel conditions. It should be understood that traditional techniquesfor propagation channel estimation may be used as needed or desired.Note that the estimation of channel coefficients represents alonger-term estimate, rather than the short-term (instantaneous)estimates that are generally used in the second mode of operation.

In any case, it should be understood that, however they are constructed,the CDF curves characterize the (expected) performance of a particularreceiver type, or types. FIG. 5 illustrates one method of characterizingreceiver performance based on CDF curves, but it should be understoodthat other methodology may be used to characterize receiver performancefor long-term and short-term propagation channel conditions.

In more detail, FIG. 5 illustrates an embodiment of a receiverperformance characterization method that may be performed usingempirical testing, software simulation, dynamic measurements, or anycombination thereof. Because different receiver types offer differentlevels of performance, such characterization is done for the particularreceiver type associated with the wireless communication device 12. (Ifthe channel quality information is generated by the wirelesscommunication device 12, the receiver performance data can be stored inthe wireless communication device 12. If the channel quality informationis generated in the base station 10, the base station 10 may storecharacterization data for different types of receivers, and use theappropriate sets of receiver performance data for different wirelesscommunication devices.)

In any case, processing begins by computing an expected error rate foreach one in a number of receiver input signal quality values, for eachone in a number of modulation and coding schemes, and for each one in anumber of propagation channel realizations (Step 120). Error rate may beexpressed, for example, as Bit Error Rate (BER), Block Error Rate(BLER), Frame Error Rate (FER), etc., and the particular manner in whicherror rate is expressed may be based on the type of data transmissionsinvolved.

As used herein, unless otherwise noted, the term “receiver input signalquality” denotes the ratio of total received signal energy per chip,E_(T), over the noise plus interference, N₀. Measurements of receiverinput signal quality represent the “raw” input signal quality for thereceiver embodied within the wireless communication device 12, and doesnot depend on the receiver's interference suppression and signal gainperformance, and thus does not depend on the accuracy of short-termpropagation channel estimates. Moreover, receiver input signal qualitymeasurements are the same for simple and complex receiver structures,e.g., the same whether the device's receiver is a simple linearreceiver, or a complex non-linear receiver.

Further, as used herein, the term “propagation channel realization”represents a particular combination of propagation channel tap weights.For example, a plurality of three-tap characterizations of thepropagation channel comprises different combinations of three complextap coefficients, corresponding to different propagation channelconditions. The different propagation channel realizations may be basedon a fixed Power Delay Profile (PDP). Alternatively, a given fast fadingrealization may be used for different PDPs, and different CDFs may beused for the different PDPs.

In any case, each propagation channel realization may be understood asrepresenting a particular hypothesis of actual propagation channelconditions for the transmit link between the base station 10 and thewireless communication device 12. For the same input signal quality, thewireless communication device 12 will exhibit different output signalquality for different channel realizations.

For each receiver input signal quality and each modulation and codingscheme, receiver performance characterization processing continues by,for each of the error rates computed, computing the data rate (R) thatcan be achieved (supported) for each propagation channel realization(Step 122). The achievable data rate, also referred to as the supporteddata rate, represents the data rate (R) that can be used fortransmitting to the wireless communication device 12 while still meetinga defined performance requirement, e.g., a BLER target. For example, ifthe computed error rate is less than the target BLER, i.e.,BLER<BLER(target), the data rate (R_(mcs)) corresponding the modulationand coding scheme can be the supported data rate (R=R_(mcs)), otherwisethe supported data rate can be zero (R=0). If ARQ is used, then thesupported data rate (R) can be calculated as R=R_(mcs)(1−BLER), whereR_(mcs) is the data rate corresponding the modulation and coding schemeand BLER is the computed error rate. If HARQ is used, then the supporteddata rate can be calculated as R_(mcs)/(1+BLER).

Processing continues by, for each receiver input signal quality,computing the cumulative distribution function (CDF) of the supporteddata rates corresponding to the propagation channel realizations (Step124). Note that the generation of CDF curves can be a one-time process,or can be wholly or partially a dynamic process. For example, as wasnoted earlier, ongoing estimation of one or more parameters bearing onthe longer-term propagation channel conditions for the wirelesscommunication device 12. Again, such parameters can include, but are notlimited to, any one or more of the PDP, estimated channel coefficients,current data service type and/or data characteristics such as packetsize, mobility/rate-of-travel estimates, etc.

FIG. 6 graphically depicts receiver performance data generated accordingto the method of FIG. 5 for a Minimum Mean Square Error (MMSE) receivertype. More particularly, FIG. 6 graphs receiver input signal quality(SNR) curves stepped from −22 dB to +12 dB in 2 dB increments overdefined data rate points, according to the CDFs of the supported datarates for the hypothesized set of propagation channel realizations. Theleftmost curve corresponds to input SNR of −22 dB, whereas the rightmostcurve corresponds to input SNR of +12 dB. FIG. 7 depicts similarperformance characterization data for a Joint Detection (JD) receiverarchitecture, and it should be understood that the particular receiverperformance data used for the wireless communication device 12 would bematched to its particular receiver type. (Further, because some types ofreceivers have different reception modes that yield differentperformance characteristics, different receiver performance data can beused in each such mode.)

In determining channel quality information using the performance curvesof FIG. 6, for example, consider the case of higher rates of travel,where the channel fading conditions become more temporally uncorrelatedbetween the measurement time at which propagation channel conditions areestimated, and the transmit time at which transmit link adaptationsbased on those channel estimates are performed. If the channelconditions are changing more rapidly than link adaptation control cankeep up with, link adaptation—e.g., transmit data rate selection—shouldbe based on the statistical propagation characteristics determined bythe path gain and shadowing, rather than based on the channel estimates.

Given signal quality measured by the wireless communication device 12,the transmit data rate can be selected from the corresponding signalquality curve in the receiver performance data, according to a desiredCDF level. For example, choosing the tenth percentile for theappropriate SNR curve corresponds to the data rate achievable forninety-percent of the hypothesized propagation channel realizations. Theparticular value to choose generally depends on the particularperformance requirements of the system, such as determined by a definedperformance requirement, like maximum tolerable BLER. In one or moreembodiments, the signal quality represents a long-term signalquality—average input SNR—as measured by the wireless communicationdevice, or as averaged by the network. In other embodiments, such aswhere channel estimates are reliable, the instantaneous or short-termreceiver input signal quality may be used.

In either case, the above approach effectively quantizes the rate valuesin the performance characterization graph to the rates represented byquantized input signal quality measurements, which is sufficient forslow link adaptation in a rapidly varying channel. That is, for fastfading conditions, the channel quality information may be generated asdata rate selections based on selecting an SNR curve from the graphcorresponding to long-term measured signal quality at the wirelesscommunication device 12, and then identifying the data rate that isachievable at a desired probability for the defined performancerequirement, e.g., for a defined BLER limit. Effectively, the methodamounts to generating channel quality information as a function oflong-term propagation channel characteristics based on mapping areceiver input signal quality measurement to a data rate selection thatis achievable at a desired probability over a range of short-termpropagation channel characteristics.

As the channel becomes more reliable, for example, when vehicle speedsbecome slower or actual input SNR at the receiver becomes larger due toimproved path gain, the channel quality information generation processcan be transitioned to a mode where more refined information isgenerated, i.e., a mode where the short-term propagation channelconditions prevailing at the wireless communication device 12 areexplicitly considered. The same performance characterization data thatwas used for slow adaptation during fast fading may be used for fastadaptation during slow fading. In other words, the same receiverperformance curves can be used for slow and fast link adaptation in ahierarchical manner. That is, channel quality metrics can be used tocharacterize the long-term properties of the channel, which can then becharacterized further for fast link adaptation when the channel becomesmore reliable.

One method for accomplishing the above operation is to quantize thechannel state values for each input signal quality (SNR) and store thequantized values in a codebook. For specific input SNR and channelestimates obtained at the wireless communication device 12, thequantized values can be looked up in the codebook, and the correspondingdata rate selected for channel quality information reporting.

FIG. 8 illustrates one embodiment of hierarchical channel qualityinformation generation, wherein the channel quality information isgenerated in terms of data rate reports. Such processing may beperformed at the wireless communication device 12, at the base station10, or cooperatively. In any case, processing begins with evaluation ofthe propagation channel conditions (Step 130). Evaluation may compriseevaluating short-term propagation channel estimates being generated bythe wireless communication device 12 as a means of determining whetherthe estimates are reliable, or may comprise checking Doppler shifts,etc.

If the channel estimates are not reliable (Step 132), a supported datarate is selected using receiver performance data, such as illustrated inFIGS. 6 and 7. More particularly, if the channel estimates are notreliable, the measured receiver input signal quality can be mapped toone of the quantized SNR curves, and a corresponding supported data ratecan be identified according to the desired probability of achieving thatrate over the range of propagation channel realizations used to generatethe performance data (Step 134). A tenth percentile selection means thatninety-percent of the hypothesized propagation channel realizations willsupport the selected data rate at the desired error rate performance.

As such, if the channel estimates are not reliable, the transmit datarate is selected probabilistically, rather than based on any specificconsideration of the short-term propagation channel conditions existentat the wireless communication device 12. Further, in cases where thechannel estimates are not reliable, the receiver input signal qualityused to select the appropriate quantized SNR curve may be a long-term(average) receiver input signal quality. Averaging may be done at thewireless communication device 12, or instantaneous values reported bythe wireless communication device 12 may be averaged by the network.

On the other hand, if the channel estimates are reliable (Step 132), themeasured receiver input signal quality may represent a shorter term,e.g., instantaneous, measurement. Of course, averaged values may stillbe used. In either case, with the availability of reliable channelestimates, the receiver input signal quality can be mapped to one of thequantized SNR curves and a particular propagation channel realization,or a constrained range of propagation channel realizations,corresponding to the channel estimates (Step 136). In one variation ofthis approach, different SNR/CDF curves can be stored for long-term andshort-term SNR measurements, with the different SNR curves reflectingdifferent probabilistic characteristics. Then, in operation, the set ofcurves to be used is selected depending on whether long-term orshort-term SNR values are being used, which may switch as a function ofchannel estimate reliability.

This hierarchical approach to channel quality information generation canbe implemented in the wireless communication device 12, such as byincluding appropriately configured processing circuits in the device 12,along with storing appropriate receiver performance data. FIG. 9illustrates one embodiment of the wireless communication device 12,configured for carrying out a method of channel quality informationgeneration using receiver performance data. The illustrated embodimentcomprises a receive/transmit antenna 20, a switch/duplexer 21, areceiver front-end 22, a transmitter 24, a baseband (BB) controller 26,a system controller 28, input/output (I/O) interface circuits 30, and auser interface (UI) 32.

Of particular interest regarding channel quality information generation,the baseband controller 26 includes one or more processing circuits 40,which are configured for channel quality information generation, andwhich have access, direct or indirect, to a memory 42 storing receiverperformance data. The stored data may comprise a data structurerepresenting quantized SNR curves and corresponding CDFs of supportedrates for a plurality of propagation channel realizations, e.g., a setof 1000 channel realizations, such as illustrated in FIG. 6 or 7.However, at least some of the performance data may be obtained usingcurve-fitting calculations—e.g., polynomials—and it should be understoodthat various methods of storing and representing receiver performancedata are contemplated herein.

In operation according to one embodiment, the wireless communicationdevice 12 maintains a long-term estimate of receiver input signalquality—average SNR—and further maintains short-term (instantaneous)propagation channel estimates. If the propagation channel estimates arenot reliable, the wireless communication device 12 operates in a firstmode of channel quality information generation. In the first mode, thewireless communication device 12 maps measured, average receiver inputsignal quality to the closest corresponding receiver input signalquality represented in the receiver performance data, and then uses thatSNR curve to identify the data rate that can be supported at a desiredprobability over a range of propagation channel realizations. As such,the wireless communication device 12 returns channel quality informationto the base station 10 in the form of updated transmit data rateselections that are identified probabilistically, without regard to theactual channel estimates. A transmit link adaptation control circuit 38in the base station 10 uses the reported data rate selections to adjustthe transmit data rate used to send traffic to the wirelesscommunication device 12.

If the propagation channel estimates are reliable, the wirelesscommunication device 12 operates in a second mode. In the second mode,the wireless communication device 12 selects the SNR value in thereceiver performance data most closely corresponding to the averagereceiver input signal quality as measured by the wireless communicationdevice 12, and further selects a propagation channel realization, or aconstrained range of propagation channel realizations, in the receiverperformance data that most closely corresponds with current channelestimates. The wireless communication device 12 thus uses the receiverperformance data to identify the data rates that can be supported formeasured receiver input signal quality and corresponding channelestimates, and reports the identified data rate selections to the basestation 10.

In both the first and second modes, the base station 10 receives channelquality information in the form of data rate selections, and the basestation 10 performs corresponding transmit data rate adjustments forforward link transmissions to the wireless communication device 12. Assuch, whether the channel quality information is being generated inconsideration of current channel estimates may be transparent to thebase station 10. That is, from the base station's perspective, linkadaptation may transparently shift between the first and second modes,without need for explicit signaling. In some embodiments, however, themode of channel quality information generation may be signaled, orotherwise indicated. For example, the rate at which channel qualityinformation is reported to the base station 10 may change in dependenceon whether channel quality information is being generated in the firstor second modes.

FIGS. 10 and 11 illustrate embodiments of processing circuits that maybe included in, or associated with, the baseband controller 40 of thewireless communication device 12, and used to implement generation ofchannel quality information in the first and second modes. FIG. 10, inparticular, illustrates the processing circuit(s) 40 as comprising achannel quality information generation circuit 44, which generateschannel quality information, e.g., rate selection data, in first andsecond modes. The circuit 44 may be configured to provide an indicationof the type of channel quality information being generated, i.e., it mayindicate the mode that it is operating in.

The processing circuit(s) 40 may further include, or may further beassociated with, a channel estimate reliability evaluation circuit 46and a channel estimation circuit 48. The channel estimate reliabilityevaluation circuit 46 is configured to estimate the reliability of thechannel estimates being generated by the channel estimation circuit 48,which generates instantaneous propagation channel estimates based on thereceived signal and pilot information. The channel estimate reliabilityevaluation circuit 46 may receive, among other things, the channelestimates from the channel estimation circuit 48 and/or the pilotvalues. Operation may be switched between the first and second modesbased on the reliability indicator output by the reliability evaluationcircuit 46.

Note, too, that the channel quality information generation circuit 44may be configured to perform the receiver input signal qualitymeasurements, i.e., the E_(T)/N₀ calculations, or another functionalcircuit may be included for that purpose in the processing circuit(s)40. On that point, it should be understood that illustrations of theprocessing circuit(s) 40 may represent functional rather than physicalcircuit elements. For example, the processing circuit(s) 40 may compriseall or a portion of a microprocessor-based circuit, an FPGA, ASIC, etc.

Continuing with function circuit descriptions, FIG. 11 illustrates oneembodiment of the channel quality information generation circuit 44 thatis depicted in FIG. 10. One sees that the reliability indicator drives amode select circuit 50, which selects the source circuit for the channelquality information being output. If the reliability indicator indicatesthat the channel estimates are not reliable, the mode select circuit 50selects a long-term channel quality information estimation circuit 52 asthe source circuit. The long-term channel quality information estimationcircuit 52 selects supported data rates using the receiver performancedata based on long-term estimates of receiver input signal quality anddesired CDF probabilities.

Conversely, if the reliability indicator indicates that the channelestimates are reliable, the mode select circuit 50 selects aninstantaneous (short-term) channel quality information estimationcircuit 54 as the source circuit. In one embodiment, the instantaneouschannel quality information estimation circuit 54 selects supported datarates using the receiver performance data based on long-term estimatesof receiver input signal quality and the channel estimates. In anotherembodiment, instantaneous channel quality information is generated bycalculating receiver output signal quality. In such embodiments, channelquality information is determined in the first mode using receiver inputsignal quality, and determined in the second mode using receiver outputsignal quality.

In any case, it should be understood that the base station 10 can beconfigured to generate channel quality information according to any ofthe above embodiments, based on the wireless communication devicefeeding back channel quality measurements. For example, FIG. 12illustrates a channel quality information generation circuit 60 and amemory 62, which may be included in the base station 10. The memory 62stores receiver performance data for one or more receiver types, with atleast one set of receiver performance data matching the type of receiverimplemented in the wireless communication device 12.

More generally, in such embodiments, the base station 10 comprises oneor more processing circuits configured to determine channel qualityinformation for a transmit propagation channel corresponding to thewireless communication device 12. Such generation may be based on, in afirst mode, generating channel quality information according to a firstalgorithm that does not depend on channel estimates for the wirelesscommunication device 12, and in a second mode, generating channelquality information according to a second algorithm that depends on thechannel estimates.

In one embodiment, in the first mode, the base station 10 receives atleast receiver input signal quality information for the wirelesscommunication device 12. As described, the first algorithm may comprisemapping receiver input signal quality to a data rate that is achievableat a desired probability over a range of propagation channelrealizations. For the second mode of operation, the base station 10receives receiver input signal quality information and propagationchannel information from the wireless communication device 12—e.g.,quantized long-term SNR values and quantized short-term propagationchannel estimates.

If the base station 10 stores code books of SNR values and propagationchannel realizations, the wireless communication device 12 need onlyreturn code book indices corresponding to its measurements. In any case,the second algorithm may comprise mapping receiver input signal qualityto a data rate that is achievable for a particular propagation channelrealization, or for a constrained range of propagation channelrealizations, corresponding to the propagation channel estimates.

As such, the base station 10 can be configured to select operation inthe first mode if it receives receiver input signal quality informationfor the wireless communication device 12 without receiving correspondingchannel estimates. Alternatively, the wireless communication device 12can be configured always to report channel estimates and signal quality,and the base station 10 can be configured to select operation in thefirst or second modes based on evaluating the reliability of the channelestimates. In at least one embodiment, the base station 10 selects themode based on determining whether the wireless communication device 12is operating in fast fading conditions. If the wireless communicationdevice 12 is operating in fast fading conditions, the base station 10operates in the first mode. If the wireless communication device 12 isnot operating in fast fading conditions, the base station 10 operates inthe second mode. Of course, it should be understood that first andsecond modes of operation may be managed independently for individualones in a plurality of wireless communication devices being supported bythe base station 10.

Further, and more generally, it should be understood that channelquality information generation as taught in one or more embodimentsdescribed herein uses receiver performance data to determine channelquality information metrics, such as supported data rates, based onusing receiver performance data. The receiver performance datacharacterizes supported data rates in terms of propagation channelrealizations, for each in a plurality of quantized receiver input signalqualities. In a first mode of operation, the data rate that can beachieved at a desired probability over a range of propagation channelconditions, e.g., all hypothesized propagation channel realizations, areselected for the receiver input signal quality value that corresponds tomeasurements obtained by the wireless communication device 12. As such,the data rate is not set in consideration of the instantaneous channelconditions prevailing at the wireless communication device 12, butrather set probabilistically, in consideration of the long-term channelconditions. As such, the first mode of operation can be selectedwhenever reliable channel estimates are not available.

In a second mode of operation, where reliable channel estimates areavailable, data rates are selected using receiver input signal qualitiesand propagation channel realizations corresponding to measurementsobtained at the wireless communication device 12. In other words,short-term propagation channel conditions are considered when theestimates of those conditions are reliable. In this regard, the samereceiver performance data can be used to generate channel qualityinformation metrics with or without using current propagation channelestimates. As such, it is convenient to modify transmit link adaptationto switch between slow link adaptation—i.e., the first mode ofoperation—and fast link adaptation—i.e., the second mode of operation.

Of course, the present invention is not limited by the foregoingdiscussion, nor is it limited by the accompanying drawings. Indeed, thepresent invention is limited only by the following claims, and theirlegal equivalents.

1. A method of determining channel quality information for a transmitpropagation channel associated with a wireless communication device, themethod comprising: in a first mode, generating channel qualityinformation according to a first algorithm that does not depend oncurrent propagation channel estimates; and in a second mode, generatingchannel quality information according to a second algorithm that dependson current propagation channel estimates.
 2. The method of claim 1,further comprising determining whether to operate in the first mode orin the second mode as a function of propagation channel fadingconditions.
 3. The method of claim 1, further comprising determiningwhether to operate in the first mode or in the second mode responsive toevaluating a reliability of propagation channel estimates made by thewireless communication device.
 4. The method of claim 1, whereingenerating channel quality information according to a first algorithmthat does not depend on current propagation channel estimates comprisesmapping a receiver input signal quality for the wireless communicationdevice to a data rate selection that is achievable at a desiredprobability over a range of propagation channel conditions.
 5. Themethod of claim 4, wherein mapping a receiver input signal quality forthe wireless communication device to a data rate selection that isachievable at a desired probability over a range of propagation channelconditions comprises using a Cumulative Distribution Function (CDF) andthe receiver input signal quality to identify a data rate that isachievable with respect to a desired error limit over a range ofhypothesized propagation channel realizations.
 6. The method of claim 5,wherein using a Cumulative Distribution Function (CDF) and the receiverinput signal quality to identify a data rate that is achievable withrespect to a desired error limit over a range of hypothesizedpropagation channel realizations comprises selecting a CDF curve thatrelates received signal quality to achievable data rates over a set ofhypothesized propagation channel realizations.
 7. The method of claim 6,further comprising generating one or more CDF curves to support mappingof the received signal quality based on estimating long-term propagationchannel conditions for the propagation channel associated with thewireless communication device.
 8. The method of claim 7, whereingenerating one or more CDF curves to support mapping of the receivedsignal quality based on estimating long-term propagation channelconditions for the propagation channel associated with the wirelesscommunication device comprises generating the one or more CDF curvesbased on one or more of long-term propagation channel estimates,rate-of-travel of the wireless communication device, type of dataservices active for or requested for the wireless communication device,downlink bandwidth assigned to or available for the wirelesscommunication device, and a modulation and coding scheme being used foror desired for the wireless communication device.
 9. The method of claim1, wherein generating channel quality information according to a secondalgorithm comprises mapping a receiver input signal quality for thewireless communication device to a data rate selection that isachievable for propagation channel conditions corresponding to thecurrent propagation channel estimates.
 10. The method of claim 1,wherein the wireless communication device generates the channel qualityinformation as feedback for transmit link adaptation.
 11. The method ofclaim 1, wherein the wireless communication device generates channelquality measurements and a base station in a supporting wirelesscommunication network generates the channel quality information based onreceiving the channel quality measurements.
 12. The method of claim 11,wherein the channel quality measurements for the first mode comprise atleast receiver input signal quality measurements, and wherein thechannel quality measurements for the second mode comprise receiver inputsignal quality measurements and corresponding propagation channelestimates.
 13. The method of claim 1, further comprising storingreceiver performance data for use in generating the channel qualityinformation in at least the first mode, said receiver performance datacharacterizing a type of receiver corresponding to the wirelesscommunication device and identifying, for each in a plurality ofreceiver input signal qualities, supported data rates for a plurality ofpropagation channel realizations.
 14. The method of claim 13, whereingenerating the channel quality information according to the firstalgorithm comprises selecting a receiver input signal qualitycorresponding to a receiver input signal quality measurement made by thewireless communication device, and identifying a data rate that can besupported for the receiver input signal quality over a range ofpropagation channel realizations.
 15. The method of claim 13, whereingenerating the channel quality information according to the secondalgorithm comprises selecting a receiver input signal qualitycorresponding to receiver input signal quality measurements made by thewireless communication device, selecting a propagation channelrealization or a constrained range of propagation channel realizationscorresponding to propagation channel estimates made by the wirelesscommunication device, and identifying a data rate that can be supportedfor the receiver input signal quality and the selected propagationchannel realization or constrained range of propagation channelrealizations.
 16. The method of claim 1, further comprising selectivelyoperating in the first and second modes as a function of at least one of(a) packet lengths of data to be transmitted by the wirelesscommunication device, (b) delay requirements associated with packet datato be transmitted by the wireless communication device, (c) delayrequirements associated with a communication service active at thewireless communication device, (d) identification of the wirelesscommunication device, and (e) network usage or congestion levels.
 17. Awireless communication device comprising one or more processing circuitsconfigured to determine channel quality information for one or moresignals received by the wireless communication device, based on: in afirst mode, generating channel quality information according to a firstalgorithm that does not depend on current propagation channel estimates;and in a second mode, generating channel quality information accordingto a second algorithm that depends on current propagation channelestimates.
 18. The wireless communication device of claim 17, whereinthe one or more processing circuits comprise a channel qualityinformation generation circuit that is configured to generate thechannel quality information by selectively operating in the first andsecond modes.
 19. The wireless communication device of claim 18, whereinthe one or more processing circuits include a reliability evaluationcircuit to generate a reliability indicator indicating whetherpropagation channel estimates being generated at the wirelesscommunication device are reliable, and wherein the channel qualityinformation generation circuit is configured to select the first mode ofoperation if the reliability indicator indicates that the propagationchannel estimates are not reliable, and to select the second mode ofoperation if the reliability indicator indicates that the channelestimates are reliable.
 20. The wireless communication device of claim17, wherein one or more processing circuits are configured to determinewhether to operate in the first mode or in the second mode according toa reliability of propagation channel estimates made by the wirelesscommunication device.
 21. The wireless communication device of claim 17,wherein the first algorithm comprises mapping a receiver input signalquality for the wireless communication device to a data rate selectionthat is achievable at a desired probability over a range of propagationchannel conditions.
 22. The wireless communication device of claim 21,wherein mapping a receiver input signal quality for the wirelesscommunication device to a data rate selection that is achievable at adesired probability over a range of propagation channel conditionscomprises using a Cumulative Distribution Function (CDF) and thereceiver input signal quality to identify a data rate that is achievablewith respect to a desired error limit over a range of hypothesizedpropagation channel realizations.
 23. The wireless communication deviceof claim 22, wherein using a Cumulative Distribution Function (CDF) andthe receiver input signal quality to identify a data rate that isachievable with respect to a desired error limit over a range ofhypothesized propagation channel realizations comprises selecting a CDFcurve that relates received signal quality to achievable data rates overa set of hypothesized propagation channel realizations.
 24. The wirelesscommunication device of claim 23, further comprising generating one ormore CDF curves to support mapping of the received signal quality basedon estimating long-term propagation channel conditions for thepropagation channel associated with the wireless communication device.25. The wireless communication device of claim 24, wherein generatingone or more CDF curves to support mapping of the received signal qualitybased on estimating long-term propagation channel conditions for thepropagation channel associated with the wireless communication devicecomprises generating the one or more CDF curves based on one or more oflong-term propagation channel estimates, rate-of-travel of the wirelesscommunication device, type of data services active for or requested forthe wireless communication device, downlink bandwidth assigned to oravailable for the wireless communication device, and a modulation andcoding scheme being used for or desired for the wireless communicationdevice.
 26. The wireless communication device of claim 17, wherein thesecond algorithm comprises mapping a receiver input signal quality forthe wireless communication device to a data rate selection that isachievable for propagation channel conditions corresponding to thecurrent propagation channel estimates.
 27. The wireless communicationdevice of claim 17, wherein the wireless communication device includesmemory storing receiver performance data for use by the one or moreprocessing circuits in generating the channel quality information in atleast the first mode, said receiver performance data characterizing atype of receiver corresponding to the wireless communication device andidentifying, for each in a plurality of receiver input signal qualities,supported data rates for a plurality of propagation channelrealizations.
 28. The wireless communication device of claim 27, whereinthe first algorithm comprises selecting a receiver input signal qualitycorresponding to a receiver input signal quality measurement made by thewireless communication device, and identifying a data rate that can besupported for the receiver input signal quality over a range ofpropagation channel realizations.
 29. The wireless communication deviceof claim 27, wherein the second algorithm comprises selecting a receiverinput signal quality corresponding to a receiver input signal qualitymeasurement made by the wireless communication device, selecting apropagation channel realization or a constrained range of propagationchannel realizations corresponding to propagation channel estimates madeby the wireless communication device, and identifying a data rate can besupported for the receiver input signal quality and the selectedpropagation channel realization or constrained range of propagationchannel realizations.
 30. A base station comprising one or moreprocessing circuits configured to determine channel quality informationfor a transmit propagation channel corresponding to a wirelesscommunication device associated with the base station, based on: in afirst mode, generating channel quality information according to a firstalgorithm that does not depend on current propagation channel estimatesfor the wireless communication device; and in a second mode, generatingchannel quality information according to a second algorithm that dependson current propagation channel estimates for the wireless communicationdevice.
 31. The base station of claim 30, wherein, in the first mode,the base station receives at least receiver input signal qualityinformation for the wireless communication device, and wherein the firstalgorithm comprises mapping receiver input signal quality to a data ratethat is achievable at a desired probability over a range of propagationchannel realizations.
 32. The base station of claim 31, wherein mappinga receiver input signal quality for the wireless communication device toa data rate selection that is achievable at a desired probability over arange of propagation channel conditions comprises using a CumulativeDistribution Function (CDF) and the receiver input signal quality toidentify a data rate that is achievable with respect to a desired errorlimit over a range of hypothesized propagation channel realizations. 33.The base station of claim 32, wherein using a Cumulative DistributionFunction (CDF) and the receiver input signal quality to identify a datarate that is achievable with respect to a desired error limit over arange of hypothesized propagation channel realizations comprisesselecting a CDF curve that relates received signal quality to achievabledata rates over a set of hypothesized propagation channel realizations.34. The base station of claim 33, further comprising generating one ormore CDF curves to support mapping of the received signal quality basedon estimating long-term propagation channel conditions for thepropagation channel associated with the wireless communication device.35. The base station of claim 34, wherein generating one or more CDFcurves to support mapping of the received signal quality based onestimating long-term propagation channel conditions for the propagationchannel associated with the wireless communication device comprisesgenerating the one or more CDF curves based on one or more of long-termpropagation channel estimates, rate-of-travel of the wirelesscommunication device, type of data services active for or requested forthe wireless communication device, downlink bandwidth assigned to oravailable for the wireless communication device, and a modulation andcoding scheme being used for or desired for the wireless communicationdevice.
 36. The base station of claim 30, wherein, in the second mode,the base station receives receiver input signal quality information andpropagation channel estimates for the wireless communication device, andwherein the second algorithm comprises mapping receiver input signalquality to a data rate that is achievable for a particular propagationchannel realization, or for a constrained range of propagation channelrealizations, corresponding to the propagation channel estimates. 37.The base station of claim 30, wherein the base station is configured toselect operation in the first mode if it receives receiver input signalquality information for the wireless communication device withoutreceiving corresponding propagation channel estimates for the wirelesscommunication device.
 38. The base station of claim 30, wherein the basestation is configured to select operation in the first mode if itdetermines that propagation channel estimates for the wirelesscommunication device are not reliable.
 39. The base station of claim 30,wherein the base station is configured to select operation in the firstmode if the wireless communication device is operating in fast fadingconditions, and is configured to select operation in the second mode ifthe wireless communication device is not operating in fast fadingconditions.
 40. The base station of claim 30, wherein the base stationincludes memory storing receiver performance data for use by the one ormore processing circuits in generating the channel quality informationin at least the first mode, said receiver performance datacharacterizing a type of receiver corresponding to the wirelesscommunication device and identifying, for each in a plurality ofreceiver input signal qualities, supported data rates for a plurality ofpropagation channel realizations.
 41. The base station of claim 40,wherein the first algorithm comprises using the receiver performancedata to select a receiver input signal quality corresponding to areceiver input signal quality measurement made by the wirelesscommunication device, and identify a data rate that can be supported forthe receiver input signal quality over a range of propagation channelrealizations.
 42. The base station of claim 40, wherein the secondalgorithm comprises using the receiver performance data to select areceiver input signal quality corresponding to a receiver input signalquality measurement made by the wireless communication device, select apropagation channel realization or a constrained range of propagationchannel realizations, corresponding to propagation channel estimatesmade by the wireless communication device, and identify a data rate canbe supported for the receiver input signal quality and the selectedpropagation channel realization or constrained range of propagationchannel realizations.
 43. A receiver performance characterization methodcomprising: for each of a number of receiver input signal qualities andeach of a number of modulation and coding schemes, computing an errorrate expected for each of a number of propagation channel realizations;for each of said receiver input signal qualities and each of saidmodulation and coding schemes, computing a data rate that can besupported for each propagation channel realization; and for eachreceiver input signal quality, computing the cumulative distributionfunction of the supported data rates corresponding to the propagationchannel realizations.
 44. The method of claim 43, wherein computing adata rate that can be supported for each propagation channel realizationcomprises determining the data rate (R) that can be supported as afunction of a data rate (R_(mcs)) corresponding to the modulation andcoding scheme, and a Block Error Rate (BLER) expected for thepropagation channel realization.
 45. The method of claim 44, whereindetermining the data rate (R) that can be supported as a function of adata rate (R_(mcs)) corresponding to the modulation and coding scheme,and a Block Error Rate (BLER) expected for the propagation channelrealization comprises calculating R as R=R_(mcs) (1−BLER).
 46. Themethod of claim 44, wherein determining the data rate (R) that can besupported as a function of a data rate (R_(mcs)) corresponding to themodulation and coding scheme, and a Block Error Rate (BLER) expected forthe propagation channel realization comprises calculating R asR=R_(mcs)/(1−BLER).
 47. The method of claim 43, wherein computing a datarate that can be supported for each propagation channel realizationcomprises determining the data rate (R) that can be supported as afunction of a data rate (R_(mcs)) corresponding to the modulation andcoding scheme, a Block Error Rate (BLER) expected for the propagationchannel realization, and a target Block Error Rate (BLER(target)). 48.The method of claim 47, wherein determining the data rate (R) that canbe supported as a function of a data rate (R_(mcs)) corresponding to themodulation and coding scheme, a Block Error Rate (BLER) expected for thepropagation channel realization, and a target Block Error Rate(BLER(target)) comprises determining R as R=R_(mcs) ifBLER<BLER(target), and otherwise determining R as R=0.
 49. A method ofproviding rate adaptation feedback from a wireless communication deviceto a supporting wireless communication network comprising storingreceiver performance data determined according to the receiverperformance characterization method of claim 30, and, in a first mode,selecting a supported data rate using the receiver performance dataaccording to a receiver input signal quality corresponding tomeasurements made by the wireless communication device and a desiredprobability of achieving the selected data rate for a range ofpropagation channel realizations, and, in a second mode, selecting asupported data rate using the receiver performance data according to areceiver input signal quality corresponding to measurements made by thewireless communication device and a particular propagation channelrealization, or a constrained range of the propagation channelrealizations, corresponding to propagation channel estimates for thewireless communication device.